• The prevalence, course, and severity of alcoholism were examined in a probability sample of homeless adults in Los Angeles' inner city and in a household sample (drawn from two communities in Los Angeles), matched to the demographic characteristics of the homeless sample. Both lifetime and current prevalence of alcoholism (as measured by the National Institute of Mental Health's Diagnostic Interview Schedule) was substantially higher among homeless individuals. Moreover, compared with household alcoholics, homeless alcoholics were characterized by (1) a substantially higher prevalence of other psychiatric disorders, particularly the major mental illnesses; (2) more severe patterns of drinking, which spanned longer periods of time; and (3) more profoundly affected levels of social and vocational functioning. Homeless alcoholics were also more likely to have entered treatment programs and to have engaged in problem behaviors as children and adults. Emphasis was placed on the complicated etiologic relationship between alcoholism and homelessness, and on the need for alcohol rehabilitation services that are sensitive to the unique situations in which homeless alcoholics find themselves.